using System;
using SunflowSharp.Core;
using SunflowSharp.Image;
using SunflowSharp.Maths;

namespace SunflowSharp.Core.Shader
{

    public class ShinyDiffuseShader : IShader
    {
        private Color diff;
        private float refl;

        public ShinyDiffuseShader()
        {
            diff = Color.GRAY;
            refl = 0.5f;
        }

        public virtual bool update(ParameterList pl, SunflowAPI api)
        {
            diff = pl.getColor("diffuse", diff);
            refl = pl.getFloat("shiny", refl);
            return true;
        }

        public virtual Color getDiffuse(ShadingState state)
        {
            return diff;
        }

        public Color getRadiance(ShadingState state)
        {
            // make sure we are on the right side of the material
            state.faceforward();
            // direct lighting
            state.initLightSamples();
            state.initCausticSamples();
            Color d = getDiffuse(state);
            Color lr = state.diffuse(d);
            if (!state.includeSpecular)
                return lr;
            float cos = state.getCosND();
            float dn = 2 * cos;
            Vector3 refDir = new Vector3();
            refDir.x = (dn * state.getNormal().x) + state.getRay().getDirection().x;
            refDir.y = (dn * state.getNormal().y) + state.getRay().getDirection().y;
            refDir.z = (dn * state.getNormal().z) + state.getRay().getDirection().z;
            Ray refRay = new Ray(state.getPoint(), refDir);
            // compute Fresnel term
            cos = 1 - cos;
            float cos2 = cos * cos;
            float cos5 = cos2 * cos2 * cos;

            Color ret = Color.white();
            Color r = d.copy().mul(refl);
            ret.sub(r);
            ret.mul(cos5);
            ret.add(r);
            return lr.add(ret.mul(state.traceReflection(refRay, 0)));
        }

        public void scatterPhoton(ShadingState state, Color power)
        {
            Color diffuse;
            // make sure we are on the right side of the material
            state.faceforward();
            diffuse = getDiffuse(state);
            state.storePhoton(state.getRay().getDirection(), power, diffuse);
            float d = diffuse.getAverage();
            float r = d * refl;
            double rnd = state.getRandom(0, 0, 1);
            if (rnd < d)
            {
                // photon is scattered
                power.mul(diffuse).mul(1.0f / d);
                OrthoNormalBasis onb = state.getBasis();
                double u = 2 * Math.PI * rnd / d;
                double v = state.getRandom(0, 1, 1);
                float s = (float)Math.Sqrt(v);
                float s1 = (float)Math.Sqrt(1.0 - v);
                Vector3 w = new Vector3((float)Math.Cos(u) * s, (float)Math.Sin(u) * s, s1);
                w = onb.transform(w, new Vector3());
                state.traceDiffusePhoton(new Ray(state.getPoint(), w), power);
            }
            else if (rnd < d + r)
            {
                float cos = -Vector3.dot(state.getNormal(), state.getRay().getDirection());
                power.mul(diffuse).mul(1.0f / d);
                // photon is reflected
                float dn = 2 * cos;
                Vector3 dir = new Vector3();
                dir.x = (dn * state.getNormal().x) + state.getRay().getDirection().x;
                dir.y = (dn * state.getNormal().y) + state.getRay().getDirection().y;
                dir.z = (dn * state.getNormal().z) + state.getRay().getDirection().z;
                state.traceReflectionPhoton(new Ray(state.getPoint(), dir), power);
            }
        }
    }
}